Ammonia adsorbing and absorbing materials can be used as solid storage media for ammonia, which in turn, for example, may be used as the reductant in selective catalytic reduction (SCR) to reduce NOx emissions of automotive vehicles, see e.g. WO 99/01205. Usually, ammonia is released from those materials by thermal desorption by means of external (see e.g. WO 99/01205) or internal (see e.g. WO 2006/012903) heating of the container containing them. In many applications this way of storing and delivering ammonia has certain advantages compared to liquid ammonia or aqueous solutions of ammonia or urea.
Metal ammine salts, which are ammonia reversibly absorbing and desorbing materials can be used as solid storage media for ammonia. WO 99/01205 uses preferably granulated Ca(NH3)8Cl2 or Sr(NH3)8Cl2 as an ammonia storage material. In WO 2006/081824 metal ammine salt forms with a high volumetric ammonia storage capacity are described.
Usually ammonia is released from the solid storage media by thermal desorption. Also, solid storage media may be exposed to high temperatures by environmental conditions. Particularly in closed systems high ammonia vapor pressures may result.